http://www.linuxppc.org/ is the home page for the Linux for PowerPC
project.

The FAQ-O-Matic is at
http://cobweb.dartmouth.edu/cgi-bin/cgiwrap/jonh/faqomatic/faq.pl.

There are web pages on Powermac/Linux at
http://www.linux-kheops.com/burpteam/mllinuxus.html and at
http://www.cs.wisc.edu/~tesch/linux_info/monLinux.info.html.

There is a lot of useful information about Linux generally at
http://www.linux.org/.

Apple has published three tech notes on Open Firmware.  They are
listed on the page at http://17.126.23.20/dev/technotes/of/of-1.html.

The IEEE 1275 Open Firmware home page is at
http://playground.Sun.COM/pub/1275/.